One of the big features is in-place OS upgrades. This allows users to upgrade from a previous version of Windows Server to a new one, while keeping their settings, features, and applications. Users will be able to use the following upgrade paths:

CURRENTLY INSTALLED OPERATING SYSTEM

AVAILABLE UPGRADE VERSION & EDITION

Windows Server 2016 Standard

Windows Server 2019 Standard or Datacenter

Windows Server 2016 Datacenter

Windows Server 2019 Datacenter

Windows Server 2012 R2 Standard

Windows Server 2019 R2 Standard or Datacenter

Windows Server 2012 R2 Datacenter

Windows Server 2019 R2 Datacenter

It's odd that Microsoft would be talking about Windows Server 2019 R2 already. It seems likely that this is just a typo.

Here's what else is new in today's build:

Storage Migration Service

A common issue around Windows Server is a lack of data migration options from older operating systems and storage platforms. Simply because in-place upgrades were impossible, and because manual migrations are slow and likely to cause significant interruptions to service or loss of access for users and applications, many customers are still using Windows Server 2012 R2, Windows Server 2008 R2, and even Windows Server 2003.

Addressing this challenge, Windows Server 2019 introduces the Storage Migration Service (SMS), a new role included in Windows Server Standard and Datacenter editions. SMS is a job-based orchestration and proxy that:

Allows administrators to inventory existing servers for their data, security, and network settings.

Migrates that data, security, and network settings to a new, modern target by using the SMB protocol.

Takes over the identity of the old server completely, while decommissioning the original source, in such a way that users and applications are unaffected and unaware that migration has taken place.

SMS provides orchestrated workflow with a Honolulu-based graphical management system, allowing scalable migrations of many servers simultaneously to new targets running on premises or in Azure.

Storage Replica

Storage Replica (SR) was first released as a technology for Windows Server 2016 Datacenter Edition. SR enables synchronous and asynchronous block replication of volumes between servers or clusters for disaster recovery. SR also enables you to create stretch failover clusters that span two sites, with all nodes staying in sync.

Beginning with Windows Server 2019, responding to customer requests, we’ve added the following improvements to SR:

Log v1.1. Performance improvements to the SR log system lead to far better replication throughput and latency, especially on all-flash arrays and Storage Spaces Direct (S2D) clusters that replicate between each other. To take advantage of this update, you must upgrade all servers participating in replication to Windows Server 2019.

Test Failover. It is now possible to mount a writable snapshot of replicated destination storage. To do so, your server must have an unused volume that is not currently replicating on the destination; on the unused volume, temporarily mount a snapshot of the replicated storage for testing or backup purposes. Replication of the original source continues unabated while you perform your tests; your data is never unprotected and your snapshot changes will not overwrite it. When you are done, discard the snapshot. (Note: We first released this feature in the Windows Server version 1709 channel).

Storage Replica Standard. SR will soon be available on Windows Server 2019 Standard Edition, not just on Datacenter Edition. When installed on servers running Standard Edition, SR has the following limitations:

SR replicates a single volume (instead of an unlimited number of volumes).

Volumes can have one partnership (instead of an unlimited number of partners). Volumes can have a size of up to 2 TB (instead of an unlimited size).

We will continue to listen to your feedback and evaluate these settings through our telemetry during Insider previews of Windows Server 2019. These limitations may change several times during the preview phase and at RTM.

This change is coming in a preview soon after Windows Server 2019, build 17639. We’re announcing these changes to seek your initial feedback. For more information about new features for Storage Replica, visit http://aka.ms/StorageReplica.

Editing or creating policies for AppLocker can cause the MMC snap-in to crash when generated rules for a packaged app.

After upgrading the operating system, the AppX database may have corrupted entries, which causes problems for components that use those entries.

Microsoft says that the two key areas that it would like feedback on are in-place OS upgrades, and app compatibility. If server roles or apps don't work like they're supposed to, you should file feedback.

As with previous builds, these will expire on July 2, 2018. It seems likely that this date will change in a future build, since this update isn't slated to be released until this fall.